1. Field of the Invention
The present invention relates to die closing units for injection molding machines, and more particularly to die closing units of the push-type, i.e. where the hydraulic cylinder which opens and closes the molding die has its axis oriented in the direction of die movement and exerts a pushing action on the movable die half during the closing stroke.
2. Description of the Prior Art
Injection molding machines having push-type die closing units are known from the prior art. One known die closing unit of this type features an arrangement in which the thrust from the power cylinder is transmitted to the movable die carrier plate by means of two piston rods, the movable die carrier plate being comparable in thickness to the stationary die carrier plate. This prior art structure thus features an arrangement in which the force acting on the power piston is transmitted to the movable die carrier plate along multiple lines of force transmission located outside the center axis of the die closing unit and arranged symmetrically with respect to the latter.
In the past, it has been the generally accepted belief among specialists in the field that it is the aforementioned pattern of force transmission lines which gives the best safety against canting of the movable die carrier plate and which, under conditions of extremely high closing pressures, assures the highest possible dimensional consistency of the injection molded parts. An additional reason why it was heretofore considered necessary to split the force transmission from the power piston to the movable die carrier plate along at least two force transmission lines spaced oppositely from the center axis of the die closing unit was the fact that only this type of arrangement would offer the necessary space for the arrangement of an ejection device, an unscrewing device, or other special accessory units which had to be mounted on the back side of the movable die carrier plate in alignment with the center axis. A die closing unit of this type is disclosed in U.S. Pat. No. 3,456,297.